On dirt you usually use blocks for set up, scales are used for asphalt racing where weight is more critical. Each chassis maker has their own blocking instructions. What kind of chassis do you have? Once you have your block heights they become your starting point to use for each race.

Steve Smith has several good books on set up I would recommend his book on midgets and or mini sprints to start with. They each have good info. They really put the old brain in gear. After reading them a dozen times or so you will probably be able to start thinking setup. You can generally find his adds in most open wheel mags.

Honest Dad himself